Compared to liquid crystal displays, organic-light-emitting-diode (OLED) displays have advantages of self-luminous property, rapid response speed, wide viewing angle, high contrast, bright color, light and thin body and so on, which are considered as a next generation of display technique. A self-luminous element (i.e., an OLED device) therein is mainly constituted by an anode layer, an organic material functional layer (normally including a functional layer such as an electron transport layer, an light emitting layer, and a hole transport layer and so on) and a cathode layer in an order of being gradually farther from a substrate. According to different emitting direction, the OLED device can be classified into two types: bottom-emitting (i.e., emitting downwards with respect to the substrate) and top-emitting (emitting upwards with respect to the substrate).
Since the cathode layer is normally constituted of a metal simple substance and/or an alloy material with a low work function, which has a low light transmittance, in order to reduce the effect of the cathode layer on the entire light extracting rate of the top-emitting OLED device, the thickness of the cathode layer needs to be made thinner, and meanwhile a reflective metal is used as the anode layer to further increase the light transmittance. However, the less the thickness of the cathode layer is, the larger a resistance Rs of its sheet resistance (whose symbol is Rs, and the expression is Rs=ρ/t; wherein, ρ is a resistivity of the electrode, t is a thickness of the electrode) is, so that a voltage drop of the top-emitting OLED device (IR Drop, i.e., a potential difference between two ends of the resistor) is severe, so that the voltage drop of the OLED light-emitting surface which is farther from a power supply location (i.e., the driving transistor connected with the anode layer) is more significant, resulting in significant uneven light emitting of the top-emitting OLED device.
In addition, since the top-emitting OLED device utilizes the cathode layer as an light exiting side, and since the light transmittance of the material constituting the cathode layer is lower, the cathode layer acts as a semi-transparent thin film with a reflection function, so that a microcavity is formed between the cathode layer and the reflective anode layer therebelow, so that the top-emitting OLED device has stronger microcavity effect, that is, the top-emitting OLED device with a specific cavity length can only emit a specific wavelength of light, so when manufacturing the top-emitting OLED device, requirements on the thicknesses of the respective layers are stricter. Thus, each of the above-mentioned factors causes current difficulty in mass production of the top-emitting OLED devices.
Thus, current OLED devices mainly utilize a bottom-emitting structure with simple manufacturing process, relatively mature technology and easy mass production, and rays are emitted from the bottom-emitting OLED run through the anode layer and are emitted from the substrate side, and the anode layer may utilize materials with a high work function and higher light transmittance such as Indium Tin Oxide (ITO) and graphene which have little influence on the light extracting rate, and no microcavity effect; meanwhile, since light is not emitted from the cathode layer side, the cathode layer will not have a too small thickness to cause a problem of too large Rs resistance.